I've visited Frugal Muse a few times and purchased one book for work there. I haven't had tons of time to browse for various reasons, but this is a pretty big bookstore with a lot of stuff. I'll echo Stacey L.'s statements and say that if you know you need a certain thing and don't have time to order it, this might not be your wisest choice. If you're just browsing, looking to score some books on the cheap, or don't need something specific and immediate, Frugal Muse works just fine.
The store is pretty well organized with just a touch of the absent-minded professorness that makes for good personality in a bookstore. The staff has been exceedingly friendly with me, and they're very knowledgeable about what's in the store and who it might be appropriate for, not just what's on the shelves.
When I was in graduate school, money was in short supply, and one thing I always missed was being able to get the personal touch of shopping in a local bookstore. Now that I have the financial stability to come back to places like Frugal Muse, I remember what I liked about them.